1. Field of the Invention
The present invention relates generally to liquid organic solvents, and more particularly, to such a solvent which effectively dissolves and removes a wide range of materials, yet which is also comparatively non-hazardous to the environment and personnel.
2. Background
Liquid solvent compositions are widely used throughout modern industry. Just a few of the many applications for such solvent compositions include the following processes: oil and grease removal; cleaning of paint guns and lines; stripping paint; washing paint rollers; cleaning and reclamation of silk screens; aluma-printing; deglazing, ink removal, and roller washing in printing processes; lacquer washing.
As is well known to those skilled in the art, the many various materials which must be solubilized in these applications differ greatly in how effectively they can be dissolved by different solvent materials. For example, the materials may be characterized as "polar" or "non-polar" (or somewhere in between) as a result of their molecular structure; it has been found that, as a general rule, "like dissolves like", so that materials having a generally polar character will tend to be most effectively solubilized by solvents also having a polar character (i.e., those solvents which rely largely on their electrical dipole characteristics for their solvent action), while materials of a non-polar character are usually more effectively solubilized by solvents which also have non-polar characteristics (i.e., those solvents which work primarily on the basis of their dispersion forces).
While it would thus in some respects be "ideal" to mate the material which is sought to be removed with a solvent which is matched to it in terms of its polar/non-polar characteristics, this is frequently not possible, or is at least impractical. For one thing, coatings and other materials may themselves be made up of both polar and non-polar constituents, and it is necessary for the solvent to be able to act on both of these in order to successfully remove the material. Furthermore, it is simply desirable from an economic and convenience standpoint to have a "general purpose" solvent available which can be relied on to perform many different cleaning tasks involving a wide variety of materials.
Unfortunately, relatively few solvent formulations have been found which are capable cleaning up a broad spectrum of materials having the varied characters discussed above. In general, the search for such general purpose solvents has focused on compounds which exhibit both polar and non-polar characteristics in a single molecule; for example, some molecules are essentially "polar" at one end, and "non-polar" at the other, in terms of their solvent characteristics. Some of these materials (e.g., fatty acids and the like, which are used in detergent mixtures) are characterized by a long-chained molecular structure, and are generally unsuitable for use in many industrial applications, due to the excessive residue which they leave behind, and the amount of rinsing or other secondary washing which is necessary to remove this.
On the other hand, a handful of organic compounds have been identified which have been successfully used as broad spectrum solvents in high technology industries, such as the aerospace and electronic industries, as well as in more commonplace applications. Unfortunately, the great majority of these have ultimately been found to present undesirable toxicologies and serious hazards to the environment; examples of these compounds include methylene chloride and methyl ethyl ketone (MEK), as well as toluene, xylene, and other aromatics, many of which include the additional hazard of high flammability. For example, although MEK has long been considered a satisfactory solvent from the standpoint of cleaning effectiveness, there is a growing concern that the toxicity and flammability of MEK exposes users to unnecessary risks. Also, because used MEK is considered a threat to the environment, and so is classified as a hazardous waste, the expense associated with the safe disposal of MEK is on the order of 5-10 times greater than the amount which the user initially pays for the solvent. Moreover, because of its relatively high vapor pressure, the loss of MEK to the atmosphere during use is excessive, necessitating the use of large and expensive collection systems such as vacuum hoods.
Because of the concern for the safety, health, and environmental hazards which these known organic solvents thus present, both the federal and state governments are promulgating increasingly stringent criteria which solvent users must comply with. For instance, the California State Legislature limits the use of volatile solvents by requiring that they have a vapor pressure below about 45 mmHg at 20.degree. C. In addition, regulations require that solvents be disposed of in a manner that will not adversely effect the environment; for many users of such solvents, this disposal generally translates into increased operating costs, as noted above.
For the above reasons, a primary consideration for many users of organic solvents has become the toxicity of a particular solvent mixture, and also the hazards which it presents to the environment. This has lead to a number of attempts to find safe substitutes for the hazardous organic solvents which have been used in the past. As an example, methylene chloride has been widely used in industry, especially for formulating paint strippers, lacquer removers, and paint clean-up systems, but it suffers from high volatility which leads to excessive evaporation, contributing to worker exposure and environmental pollution. Attempts have consequently been made to replace methylene chloride using various, safer organic solvents, but for the most part these efforts have not yielded solvent compositions which are sufficiently effective or quick in action to gain acceptance, and, furthermore, many of the proposed substitutes have proven too costly to be economically feasible. For example, n-methyl-pyrrolidone (NMP) has sometimes been found to be a suitable substitute for MEK or methylene chloride in terms of its solvent abilities, and it exhibits a very low volatility which drastically reduces the flammability hazard and evaporative losses. However, but the cost of NMP renders its use prohibitive in the concentrations which are necessary to make many of the proposed formulations perform effectively as solvents. Furthermore, NMP is excessively harsh for many applications, in that it will cause damage to the underlying substrate; for example NMP can cause severe deterioration of rubber and plastics, such as PVC. It also tends to cause irritation and defatting of user's hands.
Accordingly, a need exists for a substantially non-toxic solvent composition which exhibits superior cleaning ability when applied to a variety of substances, and which exhibits low flammability and a relatively low vapor pressure so as to limit evaporative losses. Furthermore, there is a need for such a solvent which safely degrades in the environment and in biological systems, and which is also sufficiently inexpensive to he economical for large scale use.